I feel like most Harry Potter masterposts just give all the books, so I made one with a bunch of other useful and fun HP-related sites.
All the Harry Potter Books Free (PDF and DOC)
Pottermore- Interactive Harry Potter Site (official)
Hogwarts is Here- Online Hogwarts School
Witch Weekly (First Issue)
Drawing Harry Potter Characters
Wizard Love- Hp-themed song
A big thanks to hermioneathena7 for adding Witch Weekly to her master post list! Check out their blog and collection of links